For energy-efficient swimming, body size is more important than body shape – such as a long neck. This was discovered by researchers at the University of Bristol. This goes against the old idea that there is an optimal body shape for low resistance in the water.

In the past 250 million years, a number of four-legged friends who were tired of life on land have returned to the sea. Today, whales over 25 meters in size and dolphins at 2.5 meters swim in the oceans. Both have streamlined bodies, so they experience little resistance as they glide through the water.

Among the extinct marine vertebrates you will also find streamlined species, such as the fish-like ichthyosaurs† But there were also aquatic animals with a less elegant body shape, such as the plesiosaurs. The plesiosaurs had a broad torso, short tail, four large fins and an exceptionally long neck. British researchers wondered whether these animals could maneuver efficiently through the water despite their clumsy shape.

Proteins with a Janus head

Proteins with a Janus head

slow long neck

The necks of some plesiosaurius species, such as the Elasmosaurus, could be as long as six meters, almost half the total body length. That long neck probably helped them catch fish, but it’s also an awkward protrusion. The idea was that that crazy shape created extra resistance, making the plesiosaurs slower than their streamlined contemporaries.

Researchers from the University of Bristol have now demonstrated that the plesiosaurs were not at a disadvantage despite their unique shape. This is apparent from computer simulations with 3D models of swimming ichthyosaurs, plesiosaurs and cetaceans. Because their bodies grew with their elongating necks during evolution, it cost them relatively no more energy to move through the water.

3D models of quadrupeds (cetaceans = cetaceans). Source: S. Gutarra Diaz

That’s how it works: the resistance that an aquatic animal experiences while swimming is caused by the friction between the water and the skin. And the larger a body, the smaller the skin surface relative to the animal’s mass.

Although a larger animal experiences more resistance in total than a smaller animal, there is less resistance per kilogram of body weight. This in turn means that he needs to expend less energy per kilogram of body weight to move forward than a smaller animal. In other words: your neck may become long, but then your torso must also become larger.

This corresponds to the fossil finds. The elasmosaurus fossils with the longest necks were indeed found to have the largest hulls, so they figured out the trick much earlier than the researchers.

Computer simulation of flow over the 3D model of an elasmosaur (plesiosaur). Source: S. Gutarra Diaz

Bigger body

The researchers also performed computer simulations for elasmosaurs with different neck lengths. It turned out that you cannot make the neck arbitrarily long. From a certain length, this body part does provide extra resistance, which can no longer be compensated with a larger body. The plesiosaurs never seem to have stretched their necks that far.

“Our research shows that large aquatic animals can afford to have crazy shapes, such as the long necks of elasmosaurs,” say professor Mike Benton from the University of Bristol. ‘But there are limits: body measurements cannot become infinitely large.’ Ultimately, you should be able to catch enough fish with your crazy long neck to provide that huge body with energy.